Some thoughts on the Exos:
I bought a 58 a few weeks ago. The Atmos 50 had been on my list for this season as the last item of my 3 heavies to be replaced, trying to go lighter. I almost bought an Atmos on closeout over the winter and am glad I waited.
I tried the Exos 46 and really wanted to be able to use it (lighter and cheaper than the 58), but my gear needs to work for a variety of conditions, as I don't have the cash to have multiple sets. The 46 would be tight for weeklong spring or fall trips in the Cascades or Seven Devils, so I had my retailer order a 58.
Man, the thing looked big when I got it. Plenty of room for everything, even in what I think of as "comfort" mode (base weight ~14.5 #, with BA Seedhouse SL2 carried solo, 3/4 Thermarest Prolite 3, WM Ultralight, etc). Still, the pack seems to cinch down to a nice compact bundle. For an summer overnight back east it might seem too big, but I usually try to get in a few good midweek multiday trips, rather than a bunch of weekenders, and love hiking around Mt. Rainier, where 3 (or 4) season weather can be expected even in high summer.
As far as durability goes, I have to keep telling myself the pack is "only" 2 pounds and change, because it almost seems overbuilt, and has a lot of bells and whistles (okay, no bells, but there is a whistle). While certainly not as burly as the beat-to-hell 19 year old Mountainsmith it replaced, or my K2 Shortbed that's been gathering dust for years now, the fabrics seems plenty tough where they need to be. I try not to be too heavy-handed with my gear these days--another reason I went with 58 rather than the 46 is so I wouldn't be stressing fabric, seems and buckles when I need to carry more. I don't do much bushwacking, but if I knew I'd be going off-trail, it seems like a packcover would be pretty cheap and light insurance against snags and scrapes.
Of course, this is all academic, as I haven't actually had the pack out yet (but soon). As the saying goes: In theory, there's no difference between theory and practice. In practice, there usually is.
Looking forward to reading trip reports from other Exos owners, and posting my own.